1. Field of the Invention
The present invention relates to an inflator for use in an air bag device, more particularly, to an inflator of a cylindrical type.
2. Description of Prior Art
An inflator for use in an air bag device for a passenger seat comprises a cylindrical casing having holes for discharging gas disposed on the peripheral surface thereof, propellant filled in the casing, booster for causing gas evolution of the propellant, an electrical ignitor for igniting the booster, and an auto ignition material having a lower firing temperature than the firing temperature of the booster. The casing is generally made of an aluminum or aluminum base alloy. The holes for discharging gas are generally sealed by a film. As gas is generated by the propellant, the film is broken by the gas pressure. The cylindrical inflator of this type is sometimes used for an air bag device for a driver seat.
As disclosed in Japanese Laid Open Patent Publication No. 1990-63951 corresponding to U.S. patent application Ser. No. 190,479 (dated May 4, 1988) now U.S. Pat. No. 4,858,951, and Japanese Laid Open Patent Publication No. 1990-74441 corresponding to German Patent Application No. DE 3824469.1 (dated Jul. 19, 1988), equivalent to U.S. Pat. No. 4,944,528, in case that the inflator of the air bag device is involved in the fire, the casing bursts due to the gas evolution of the propellant if the rigidity of the casing is decreased prior to the initiation of the gas evolution,of the propellant. In the inflator of this type, an auto ignition material is disposed to initiate the gas evolution of the propellant before the rigidity of the casing is extremely decreased in case that the inflator is involved in the fire and its ambient temperature is risen. In the event of fire, the auto ignition material ignites first to generate heat and then the booster ignites by the heat. As a result of this, the propellant initiates the gas evolution.
In the event of a collision of a vehicle, an electrical ignitor provided besides the auto ignition material ignites the booster.
In the conventional inflator for the air bag device, because holes for discharging gas are disposed only on one side of the peripheral surface of the casing, the gas is spouted in one direction so that the inflator receives a force in the fire during transportation or storage of the inflator.